1. Field of the Invention
This invention relates to containers and processes for making them, and more particularly to the provision of low cost containers for use in storing and heating comestibles intended for final preparation in microwave ovens.
2. Description of the Prior Art
Microwave ovens have been a boon for quick preparation of comestibles in homes, institutions and automats. The recent increased popularity of these ovens has created a large market for economical containers which, because of the plurality of functions which must be performed and variety of environments which may be encountered, must be capable of withstanding a unique combination of stresses.
The microwave oven permits extremely rapid heating, but by its very nature presents problems. Variability of optimum cooking times for different recipes is encountered where the applied microwave energy heats different materials at different rates depending upon their composition and geometry. Moreover, while one of the advantages of microwave cooking is that the same container can, in theory, be used for both storage and heating, the advantage is lost where the price of the container becomes excessive. The container must be strong at virtually all temperature conditions from below freezing to above boiling. The container must also have a moisture barrier effective at all temperatures yet be in compliance with all regulatory requirements.
Existing containers which have been suggested for use with microwave oven food preparation, have various disadvantages Existing trays made from plastic coated paperboard provide difficulties because they do not present a continuous interior surface when made as a folded carton and create difficulties in shaping a smooth flat flange for adhering a lid when stamped from a flat sheet as in the manufacture of aluminum trays. Where less expensive materials such as molded pulp are considered, these materials do not have a continuous barrier which is necessary for holding certain products such as those containing aqueous and fatty materials. The barrier is also important from the standpoint of preventing bacterial contamination of the food product. Existing containers made from molded plastic materials do not have the desirable combination of low cost and high strength necessary for the wide variety of comestibles and applications for which they would be desired. Aluminum trays, while having the necessary formability, moisture and fat barrier, as well as the desired structural strength required for microwave food product, storage and cooking applications, may present the difficulty that they reflect microwaves prefenting them from getting through to the food contents from the bottom and sides of the tray, resulting in only localized and slow heating of the food from the open top. In addition, in the case of the older models of microwave ovens, if a larger tray containing a relatively small amount of food is used, the excess reflected energy can damage the oven's microwave generation or even cause arcing from the tray to the oven.
Thus, what the art requires is an improved container for use in storing and heating comestibles intended for final preparation in microwave ovens and a simple process for preparing it. The new container should be low in cost and yet have high structural strength, provide a good moisture barrier, and enable ease of formation into the intended final shape. The desired container should also provide for optimal sizing of various compartments in the container to assure optimal cooking times for each material packaged, considering the possibility that a number of different food items might be packaged in the same container but yet require different exposure to the microwave energy. The process must lend itself to the production of containers having these and other attributes. Importantly, to insure low cost, the process must lend itself to continuous operation, and desirably should make changing of container size or shape a simple matter not requiring long down times or expensive adjustment or retooling.